Fluids based on fluorocarbon compounds are widely used in systems for heat transfer by vapor compression, notably air conditioning equipment, heat pumps, devices for refrigeration or for freezing. These devices have in common that they are based on a thermodynamic cycle comprising vaporization of the fluid at low pressure (in which the fluid absorbs heat); compression of the vaporized fluid to a high pressure; condensation of the vaporized fluid to liquid at high pressure (in which the fluid gives up heat); and expansion of the fluid to end the cycle.
The choice of a heat transfer fluid (which may be a pure compound or a mixture of compounds) is dictated on the one hand by the thermodynamic properties of the fluid, and on the other hand by additional constraints. Thus, a particularly important criterion is the effect that the fluid considered has on the environment. In particular, chlorinated compounds (chlorofluorocarbons and hydrochlorofluorocarbons) have the disadvantage that they damage the ozone layer. Therefore from now on generally nonchlorinated compounds are preferred, such as hydrofluorocarbons, fluoroethers and fluoroolefins.
Another environmental constraint is the global warming potential (GWP). It is therefore essential to develop heat transfer compositions having a GWP as low as possible, and with good energy performance.
Document WO 2006/094303 describes a large number of heat transfer compositions comprising fluoroolefins, and notably 2,3,3,3-tetrafluoropropene (HFO-1234yf), and additional compounds.
Document WO 2007/126414 describes a large number of mixtures of heat transfer compounds, and notably mixtures comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf) and ammonia.
Documents WO 2008/009928 and WO 2008/009922 describe heat transfer compositions based on pentafluoropropene, tetrafluoropropene and at least one additional compound, which may be ammonia.
Document US 2006/0243945 describes a large number of mixtures of heat transfer compounds, and notably quaternary compositions based on HFO-1234yf, ammonia, difluoromethane (HFC-32) and trifluoroiodomethane.
Document EP 2487216 describes azeotropic or quasi-azeotropic binary compositions of HFO-1234yf and ammonia.
The mixture of HFO-1234yf and ammonia represents an advantageous composition, notably for heat transfer applications—in particular because HFO-1234yf is a very interesting compound in view of its low GWP and its good energy performance. However, the miscibility of the two compounds is limited. Thus, the azeotropic mixture consisting of 78% of HFO-1234yf and 22% of ammonia undergoes demixing at a temperature less than or equal to about −21° C.
It is therefore desirable to develop compositions based on HFO-1234yf and ammonia having improved miscibility.